One large or two small?

In The Motor Ship, September 1963, the debate raged on about large bore marine diesel engines. Then, as now, there was discussion about whether a single large engine was a more economic and safer option than two smaller units.

The waters were further clouded by the announcement of a contract awarded to Swan Hunter by the British & Commonwealth Shipping Co for two of the most powerful cargo liners so far envisaged. The ships were for operation between the UK and South Africa, would each be of 10,200dwt, with a required service speed of 22.5 knots. The necessary installed power had been calculated at 35,000bhp, and tenderers were given the opportunity to propose either a single screw diesel or turbine plant, or a twin-screw diesel installation of the same power.

The winning bid employed large-bore diesel technology, but two engines rather than one. The pair of Sulzer 8RD90 engines was thought to provide a substantial reserve of power, giving the capability of speeds well in excess of the specified 22.5 knots. The article suggested the installation would be technically demanding, with a considerable amount of machinery, including refrigeration plant, having to be fitted in a relatively small space, which because of the fine lines required would be restricted in width.

In contrast to today’s vogue for fuel-miserly slow steaming, our predecessors forecast a move towards still higher speeds for cargo ships, the extra number of round trips that could be achieved justifying the extra initial expenditure. Unlike now, the additional fuel consumption was not seen as a drawback, beyond the necessary greater fuel capacity. As well as quicker transit times, more efficient cargo handling would be needed to reduce time in port, but the biggest challenge was seen as machinery reliability, with less available time for maintenance.

Indeed, in a further lead article, it was stated: “Fuel economy remains a strong feature of the diesel engine, but this could assume diminished importance over the years. Most large marine engines have recently been modified to enable maintenance work to be undertaken quickly and with the minimum of manual effort, but the most important line of development… is to prolong the period of operation between overhaul.” As an example of what could be achieved, a B&W engine that had exceeded 10,000 hours without overhaul.

Among the ships described was the Johann Schulte, said to be the “world’s largest car carrier”. It bore little resemblance to today’s slab-sided PCTC ro-ro ships, looking more like a geared bulker. Indeed, that is essentially what it was, being built to export Volkswagen Beetle cars from Germany and return with grain and ore cargoes. The 22,830dwt Johann Schulte had seven equal-length holds, with hoistable car decks in each, capable of transporting 1,750 VWs. Each pair of derricks had been adapted for handling motor vehicles in addition to bulk cargo. The engine was a Borsig-Fiat B759S two-stroke of 12,600bhp at 135rpm, with three Brown-Boveri turbochargers.

Not all the engines being produced were of large bore. The smallest size in the Sulzer RD range was of 560mm bore, and the first British-built example of this type had just been completed at Scotts of Greenock. The six-cylinder engine, rated 833bhp/cylinder at 170rpm MCR, was destined for a 4,550dwt cargo liner being built at Burntisland. One notable feature remarked upon was that the lowest SFOC, of 159kg/bhph, was recorded on test at MCR.